System and method for dynamic vertebral stabilization

ABSTRACT

An intervertebral stabilization device and method is disclosed. The device preferably includes a planar spring enclosed within a housing. The housing is joined to an articulation component at either end, and the articulation components have couplings connectable to anchoring components which are securable to adjacent vertebrae. The planar spring can flex and retract providing relative motion between the adjacent vertebrae. The articulation components are ball and socket joints which allow the entire assembly to flexibly follow the curvature of the spine. A fusion rod with articulation components and couplings at either end may be substituted for the spring device. The couplings enable interchangeability between a fusion rod assembly and spring assembly, so that dynamic stabilization can occur at one vertebral level and fusion at the adjacent vertebral level. An overhung spring assembly with a sideways displaced housing which allows for a shorter pedicle to pedicle displacement is also disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 60/732,265 filed Oct. 31, 2005, the disclosure of whichis hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to orthopedic medicine, and moreparticularly to systems and methods for restricting relative motionbetween vertebrae.

Unfortunately millions of people experience back pain, and such is notonly uncomfortable, but can be particularly debilitating. For example,many people who wish to participate in sports, manual labor, or evensedentary employment are unable to do so because of pains that arisefrom motion of or pressure on the spinal column. These pains are oftencaused by traumatic, inflammatory, metabolic, synovial, neoplastic anddegenerative disorders of the spine.

In a normal spinal column, intervertebral discs that separate adjacentvertebrae from each other serve to provide stiffness that helps torestrain relative motion of the individual vertebrae in flexion,extension, axial rotation, and lateral bending. However, a damaged discmay provide inadequate stiffness along one or more modes of spinalmotion. This inadequate stiffness may result in excessive relativevertebral motion when the spine is under a given load, as when thepatient uses the muscles of the back. Such excessive relative motion maycause further damage to the disc, thereby causing back pain andultimately, requiring replacement of the disc and/or other operations todecompress nerves affected by central, lateral or foraminal stenosis.

Heretofore, some stabilization devices have been proposed to restrict,but not entirely prevent, relative motion between adjacent vertebrae.These devices often contain linear springs that are too long to beeasily positioned between adjacent vertebrae. Thus, they are oftenimpossible to implant on motion segments where there is a shortpedicle-to-pedicle displacement. Furthermore, known spinal implantstypically have components that are either flexible, allowing limitedrelative motion between adjacent vertebrae, or rigid, providing fusionbetween vertebrae. Thus, they do not provide for interchangeabilitybetween flexible and rigid components. Accordingly, symptoms that wouldnormally indicate stabilization and fusion of adjacent motion segmentscannot be adequately treated, and vice versa. In other words, revisionof an implant to provide fusion in place of stabilization is typicallynot feasible. Finally, many devices, when implanted in multiple levelsalong the spine, do not flexibly follow the natural curvature of thespine. Such devices may therefore cause discomfort, or restrict spinalmotion in an unpredictable and unnatural manner.

Therefore, there exists a need for a system and method which correctsthe above-noted shortcomings and allows for dynamic vertebralstabilization to restore normal movement and comfort to a patient.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a stabilization system forcontrolling relative motion between a first vertebra and a secondvertebra. In accordance with this first aspect, on embodimentstabilization system may include a first stabilizer having a firstcoupling adapted to be attached to a first anchoring member, a secondcoupling adapted to be attached to a second anchoring member and aresilient member configured to be coupled to the first and secondcouplings to transmit resilient force between the first and secondcouplings, the resilient member including a planar spring, wherein atleast a portion of the planar spring flexes out-of-plane in response torelative motion between the vertebrae.

In other embodiments of the first aspect, the first stabilizer mayfurther include a casing including a hollow first member and a hollowsecond member, wherein the resilient member is positioned within acavity defined by engagement of the first and second hollow members. Theresilient member is may also be positioned inside the casing such thatthe casing limits relative motion of the vertebrae by limitingdeflection of the planar spring. The system may also include the firstanchoring member and the second anchoring member, where the first andsecond anchoring members include a yoke polyaxially coupled to afixation member implantable in a portion of either the first or secondvertebra. The system may also include a first rigid connector includingfirst and second couplings adapted to be attached to one of the firstand second anchoring members, wherein the couplings are substantiallyrigidly connected together. In other embodiments, the path followed bythe planar spring may be generally spiral-shaped, wherein the planarspring includes a central portion attached to the first coupling and aperipheral portion attached to the second coupling. The first stabilizermay further include a first articulation component configured toarticulate to permit polyaxial relative rotation between one of thefirst or second couplings. The first articulation component may includea semispherical surface and a socket within which the semisphericalsurface is rotatable to permit polyaxial motion between the resilientmember and the first anchoring member. The resilient member may becoupled to the first and second couplings such that the resilient memberis able to urge the first and second couplings to move closer togetherand is also able to urge the couplings to move further apart.

The stabilization system may include a second component comprising athird coupling and a fourth coupling, wherein the third coupling isadapted to be attached to the first anchoring member such that the firstanchoring member is capable of simultaneously retaining the first andthird couplings. The second component may be a rigid connector, whereinthe third and fourth couplings are substantially rigidly connectedtogether, or the second component may be a second stabilizer comprisinga second resilient member configured to exert resilient force betweenthe third and fourth couplings.

Another aspect of the present invention is another stabilization systemfor controlling relative motion between a first vertebra and a secondvertebra. In accordance with this second aspect, the stabilizationsystem may include a first stabilizer having a first coupling adapted torest within a yoke of a first anchoring member, a second couplingadapted to rest within a yoke of a second anchoring member, a resilientmember coupled to the first and second couplings to transmit resilientforce between the first and second couplings, the resilient memberincluding a planar spring, wherein at least a portion of the planarspring flexes out-of-plane in response to relative motion between thevertebrae and a first articulation component configured to articulate topermit relative rotation between the first stabilizer and one of thefirst or second couplings.

Still another aspect of the present invention is a stabilization systemfor controlling relative motion between a first vertebra and a secondvertebra. The stabilization system according to this aspect may includea first stabilizer having a first coupling adapted to be attached to afirst anchoring member, a second coupling adapted to be attached to asecond anchoring member, a resilient member configured to be coupled tothe first and second couplings to transmit resilient force between thefirst and second couplings, the resilient member including a planarspring, wherein at least a portion of the planar spring flexesout-of-plane in response to relative motion between the vertebrae, afirst articulation component configured to articulate to permit relativerotation between the first and second couplings and a first rigidconnector including third and fourth couplings adapted to be attached tothe first and second anchoring members, wherein the third and fourthcouplings are substantially rigidly connected together.

Yet another aspect of the present invention is a method for controllingrelative motion between a first vertebra and a second vertebra. Inaccordance with this aspect, the method may include the steps ofpositioning a planar spring of a first stabilizer attaching a firstcoupling of the first stabilizer to the first vertebra and attaching asecond coupling of the first stabilizer to the second vertebra, wherein,after attachment of the couplings to the vertebrae, the planar spring ispositioned to transmit resilient force between the vertebrae via flexureof at least a portion of the planar spring out-of-plane.

Yet another aspect of the present invention is another method forcontrolling relative motion between a first vertebra and a secondvertebra. In accordance with this aspect, the method may includeselecting a component selected from the group consisting of a firststabilizer and a first rigid connector, wherein the first stabilizercomprises a first coupling, a second coupling adapted to be attached toa second anchoring member secured to the second vertebra, a resilientmember configured to transmit resilient force between the first andsecond couplings, and a first articulation component configured toarticulate to permit relative rotation between the first and secondcouplings, wherein the first rigid connector comprises a first couplingand a second coupling substantially rigidly connected to the firstcoupling, attaching a first coupling of the selected component to afirst anchoring member secured to the first vertebra and attaching asecond coupling of the selected component to a second anchoring membersecured to the second vertebra.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the subject matter of the presentinvention and the various advantages thereof can be realized byreference to the following detailed description in which reference ismade to the accompanying drawings in which:

FIG. 1 is a perspective view of a dynamic stabilization assemblyaccording to one embodiment of the invention.

FIG. 2 is an enlarged perspective view a stabilizer of the dynamicstabilization assembly of FIG. 1.

FIG. 3 is an exploded perspective view of the stabilizer of FIG. 2.

FIG. 4 is a further exploded perspective view of the stabilizer of FIG.2.

FIG. 5 is a partially exploded perspective view of the stabilizer ofFIG. 2 having two end caps.

FIG. 6 is a perspective view of the stabilizer of FIG. 2, illustratingattachment of one end cap to an end coupling.

FIG. 7 is a perspective view of the stabilizer of FIG. 2 with attachedend caps.

FIG. 8 is a partially exploded perspective view of the dynamicstabilization assembly of FIG. 1.

FIG. 9 is a perspective view of two of the stabilizers of FIG. 2, placedend to end, with two end caps being detached therefrom.

FIG. 10 is a perspective view of two of the stabilizers of FIG. 2,placed end to end, with two end caps being attached thereto.

FIG. 11 is a perspective view of two stabilizers of FIG. 2, placed endto end, illustrating the coupling of the ends of the stabilizers to eachother.

FIG. 12 is a perspective view of the stabilizer of FIG. 2, coupledend-to-end with a second stabilizer for multi-level vertebralstabilization.

FIG. 13 is a perspective view of the two stabilizers of FIG. 12,illustrating how the articulation components may be used to provide anoverall curvature to the assembled modules.

FIG. 14 is a perspective view of the stabilizer of FIG. 2, coupledend-to-end with a rigid connector and an end cap for single levelvertebral joint stabilization with joint immobilization at an adjacentlevel.

FIG. 15 is an exploded perspective view of the stabilizer and rigidconnector of FIG. 14, illustrating the coupling of the stabilizer andthe rigid connector to each other.

FIG. 16 is a perspective view of the stabilizer and rigid connector ofFIG. 14, illustrating how the articulation components may be used toprovide an overall curvature to the assembled modules.

FIG. 17 is a perspective view of another dynamic stabilization assemblyaccording to an alternative embodiment of the invention.

FIG. 18 is an enlarged perspective view of a stabilizer and endcouplings of the dynamic stabilization assembly of FIG. 17.

FIG. 19 is an exploded perspective view of the stabilizer of FIG. 18.

FIG. 20 is an exploded perspective view of the stabilizer and endcouplings of FIG. 18.

FIG. 21 is a partially exploded perspective view of the dynamicstabilization assembly of FIG. 17.

FIG. 22 is a perspective view of an overhung stabilizer and articulatingcomponent of an overhung dynamic stabilization assembly designed forshorter pedicle-to-pedicle displacements.

FIG. 23 is an exploded perspective view of the overhung stabilizer ofFIG. 22.

FIG. 24 is a partially exploded perspective view of an overhung dynamicstabilization assembly including the components of FIG. 22.

FIG. 25 is another partially exploded perspective view of the overhungdynamic stabilization assembly of FIG. 24.

FIG. 26 is a perspective view of a fully assembled overhung dynamicstabilization assembly of FIG. 24.

FIG. 27 is a perspective view of the dynamic stabilization assemblyincluding the stabilizer of FIG. 22, along with the overhungstabilization assembly of FIG. 24.

FIG. 28 is an exploded perspective view of the dynamic stabilizationassembly of FIG. 27.

FIG. 29 is a further exploded perspective view of the dynamicstabilization assembly of FIG. 27.

DETAILED DESCRIPTION

The present invention relates to systems and methods for stabilizing therelative motion of spinal vertebrae. Those of ordinary skill in the artwill recognize that the following description is merely illustrative ofthe principles of the invention, which may be applied in various ways toprovide many different alternative embodiments. This description isunderstandably set forth for the purpose of illustrating the generalprinciples of this invention and is not meant to limit the inventiveconcepts in the appended claims.

Referring to FIG. 1, one embodiment of a single level dynamicstabilization system 10 is shown. The dynamic stabilization system 10preferably includes a stabilizer 12, a pair of fixation members 14, apair of yokes 16 securable to the fixation members 14, and a pair of setscrews 18. The fixation members 14, yokes 16, and set screws 18 may beany of a variety of types known and available in the art, or mayoptionally be specially designed for operation with the stabilizer 12.Each fixation member 14 with its corresponding yoke 16 and set screw 18provides an anchoring member 19 designed to anchor the stabilizer 12 toa pedicle or other portion of a vertebra (not shown). In the embodimentsdescribed and illustrated herein, the fixation members 14 arerepresented as pedicle screws. However, they could also be other typesof screws fixed to other parts of the vertebrae, pins, clips, clamps,adhesive members, or any other device capable of anchoring thestabilizer to the vertebrae. Additionally, each yoke 16 may be unitarilyformed with a fixation member 14 as illustrated herein, or each yoke 16may be a separate entity and be polyaxially securable to a fixationmember 14.

The stabilizer 12 is illustrated alone in FIG. 2. As shown in thatfigure, stabilizer 12 includes a central spring casing 22, and a shortarm 26 extending from the spring casing 22 on one side to anarticulation component 24. On the opposite side, a longer arm 27 extendsfrom the spring casing 22 to another articulation component 25. An endcoupling 28 is also preferably located on the outside of eacharticulation component 24, 25. It is noted that the particularconstruction of stabilizer 12 depicted in FIG. 2 may vary. For example,the short arm 26 and longer arm 27 may be flipped to opposite sides.

Referring to FIG. 3, an exploded view of the stabilizer 12 is shown,thereby illustrating the inner components of the stabilizer. Forexample, a planar spring 20 is shown encased within the spring casing22. The planar spring 20 is preferably coiled in a planar spiral-likeshape and has a threaded inner ring surface 30 and an outer ring surface32. In addition, the spring casing 22 is made up of two concentrichollow members, an inner hollow member 40 and an outer hollow member 42,with the planar spring 20 being disposed within the inner hollow member40. A circular bore 44 occupies the center of the inner hollow member40, creating a round opening from an inside surface 46 to an outsidesurface 48. A protruding circular lip 49 may also surround the bore 44where it exits the outside surface 48. An inner wall 52 of the lip 49 ispreferably threaded. Similarly, a circular bore 54 occupies the centerof the outer hollow member 42, creating a round opening from an insidesurface 56 to an outside surface 58. A protruding circular lip 59 mayalso surround the bore 54 where it exits the outside surface 58.

Shown adjacent to the inner hollow member 40 is the short arm 26, whichhas a threaded outer surface 76 on the end closest to the inner hollowmember 40. This end terminates at a flat end 36. Both surface 76 andflat end 36 are best shown in FIG. 4. On the opposite end of the shortarm 26 is the articulation component 24, which terminates at the endcoupling 28. Adjacent to the outer hollow member 42 is the long arm 27,which has a threaded terminal segment 78 on the end closest to the outerhollow member 42. The terminal segment terminates at a flat end 37 (bestshown in FIG. 4). On the opposite end of the long arm 27 is thearticulation component 25, which terminates at the end coupling 28.

When assembled, the short arm 26 fits inside the bore 44 of the innerhollow member 40. The threads on the outer surface 76 engage with thethreads on the inner wall 52, thereby securing the pieces together. Asmentioned above, the planar spring 20 fits inside the inner hollowmember 40. In addition, the long arm 27 fits through the bore 54 of theouter hollow member 42, with the threaded terminal segment 78 engagingthe threaded inner ring surface 30 of the planar spring 20. The innerhollow member 40 fits concentrically within the outer hollow member 42,with the planar spring 20 also being disposed inside. Inside of thehollow members 40, 42, the flat ends 36, 37 of the arms 26, 27 arepreferably adjacent to one another but not touching.

When assembled with the hollow members 40, 42 and the arms 26, 27, theplanar spring 20 can, if acted upon, flex out of the plane within whichit is coiled. When the longer arm 27, to which the planar spring 20 isengaged, moves toward or away from the short arm 26, the spiral-likeshape of the planar spring 20 preferably extends out of its plane. Whenthe longer arm 27 returns to its original position, the planar spring 20also preferably recoils back to its plane. During this extension andrecoil, the inside surface 46 of the inner hollow member 40, and theinside surface 56 of the outer hollow member 42 act as barriers to limitthe movement of the planar spring 20.

Use of the planar spring 20, as opposed to a longer helical spring,keeps the overall length of the stabilizer 12 relatively short. Inalternative embodiments, a planar spring according to the invention neednot have a spiral-like shape, but can rather be a cantilevered leafspring, a flexible disc, or the like. Further, in other alternativeembodiments, a planar spring need not be used; rather, a different typeof spring or a conventional helical spring may be used.

FIG. 4 illustrates the articulation components 24, 25 in an explodedview. As is mentioned above, the articulation component 24 is locatedadjacent to and couples with the inner hollow member 40, and thearticulation component 25 is located adjacent to and couples with theouter hollow member 42. Each articulation component 24, 25 preferablycomprises a semispherical surface 60, a cup 62, which are both enclosedby the end coupling 28. The cup 62 is preferably dish shaped, with acylindrical support wall 64 and two ends. On one end of the cup 62 is adepression 66, and on the opposite side of the cup 62 is a flat end 68.The semispherical surface 60 preferably has a round side 70 whichrotatably fits inside the depression 66, so that each of thearticulation components 24, 25 thus takes the form of a ball-and-socketjoint. The opposite side of each semispherical surface 60 is aconnecting side 72 which narrows into a neck 74. The neck 74 preferablywidens into either the short arm 26 or the long arm 27, which extendsaway from the semispherical surface 60 on the opposite side from theround side 70. As is discussed above, the outer wall 76 of the short arm26 is threaded, as is the terminal segment 78 of the long arm 27. Inalternative embodiments, articulation components may be omitted, or maybe formed by any other type of mechanical joints known in the art.

The end coupling 28 has a support wall 102 which forms the outer sidesof the cup, and a base 104. A circular hole 106 occupies the center ofthe base 104, and where the edge of the hole 106 meets the base 104, acircular rim 108 preferably surrounds the hole 106. The inside diameterof the rim 108 is preferably less than the diameter of the semisphericalsurface 60 of the articulation components 24 and 25, so that whenassembled the semispherical surface 60 will fit into the end coupling 28but not be capable of passing through the hole 106. At the opposite endfrom the base 104, the support wall 102 terminates in a flat edge 110.Protruding from the edge 110 in the same plane as the support wall 102,such that they form continuations of the support wall 102, is aplurality of irregularly shaped teeth 112. Between each tooth 112 andthe adjacent tooth is a notch 114.

When assembled, the round side 70 of each semispherical surface 60rotatably rests in the depression 66 of the cup 62, and the arm 26 or 27extends away from the joining side 72 of the semispherical surface 60.The generally cup-shaped end coupling 28 fits over each semisphericalsurface, arm and cup assembly. Each arm 26, 27 extends from itssemispherical surface 60 through its respective hole 106. As describedabove, the arms then extend into the spring casing 22, the long arm 27connecting to the planar spring 20 and the short arm 26 connecting tothe inner hollow member 40. Rotation of either semispherical surface 60results in movement of its arm 26, 27. When the short arm 26 moves, theflat end 37 of the opposite arm 27 may optionally contact the flat end36 of the short arm 26 to acts as a stop to limit excessive movement.Similarly, when the long arm 27 moves, the flat end 36 of the oppositeshort arm 26 may stop excessive movement via contact with the flat end37 of the long arm 27. Thus the articulation components 24, 25 securethe arms 26, 27 in a rotatable manner to the spring casing 22 to permitthe stabilizer 12 to obtain a variable curvature.

The assembled stabilizer 12 can be rotated into locking engagement withend caps or end couplings of other stabilizers for multi-levelapplication. In fact, FIG. 5 illustrates one coupled stabilizer 12,having a coupled end cap 120 and an uncoupled end cap 120. Each end cap120 preferably has a general cup-shape, much like each end coupling 28.Each end cap 120 preferably includes a support wall 122 which forms theouter sides of the cup, and a solid base 124 which forms the bottom ofthe cup. The inside diameter of the end cap 120 is sized to fit aroundeither arm 26, 27. At an opposite end from the base 124, the supportwall 122 terminates in a flat edge 130. Protruding from the edge 130 inthe same plane as the support wall 122, such that they formcontinuations of the support wall 122, are a plurality of irregularlyshaped teeth 132. Between each tooth 132 and the adjacent tooth is anotch 134.

Referring to FIG. 6, an end cap 120 is illustrated in partial engagementto a stabilizer 12. When an end cap 120 is to be attached to an endcoupling 28, the end cap 120 is preferably lined up with the endcoupling 28 so that the teeth 112, 132 are pointed toward one another.The end cap 120 is then rotated and moved toward the end coupling 28 sothat the teeth 132 fit into the notches 114, while the teeth 112 fitinto the notches 134. When the teeth 112, 132 are fully seated in thenotches 114, 134 such that the teeth 132 touch the edge 110 and theteeth 112 touch the edge 130, the end cap 120 is further rotated untilthe teeth 112, 132 interlock with each other and the end cap 120 islocked in place. A stabilizer 12 with two end caps 120 each fullyengaged on opposite ends of the stabilizer 12 is depicted in FIG. 7. Inthis depiction, the end caps 120 have been fully rotated so that theteeth 132 of the end caps 120 are interlocked with the teeth 112 of bothend couplings 28.

FIG. 8 shows an exploded view of the dynamic stabilization system 10with a fully assembled stabilizer 12, two anchoring members 19 withyokes 16 and fixation members 14, and two set screws 18. In this design,each fixation member 14 preferably has a pointed end 140 which aids inscrewing the member into a corresponding vertebra when implanted. Theopposite end of the fixation member 14 is preferably unitarily formedwith a U-shaped yoke 16, so that the bottom of the U is a head 142 ofthe fixation member 14. Each yoke 16 has two curved opposing supportwalls 144. Alternating between the support walls 144 are two opposinggaps 146, which form a cavity 148 therebetween that occupies theinterior of the yoke 16. The inner surfaces 150 of the support walls 144are also preferably threaded to engage a set screw 18.

According to the embodiment depicted, in use, the stabilizer 12 isinserted into the yokes 16 of two anchoring members 19 whose fixationmembers 14 have previously been anchored in the pedicles, or otherportion, of the corresponding vertebrae. The stabilizer 12 is laidlengthwise into the yokes 16 such that the long axis of the stabilizer12 is perpendicular to the long axes of the fixation members 14, and sothat the spring casing 22 lies between the anchoring members 19. Eachend coupling 28/end cap 120 pair preferably rests on the head 142 withinthe cavity 148. Each end cap preferably occupies the gaps 146, and thetwo articulation components 24, 25 lie adjacent to, but outside of, thetwo interior gaps 146.

The end couplings 28 and attached end caps 120 are preferably securedwithin the yokes 16 of the anchoring members 19 through the use of theset screws 18. One set screw 18 is screwed into the top of each yoke 16so that its threads engage with the threaded inner surfaces 150 of thesupport walls 144. The set screws 18 are then tightened to hold thestabilizer 12 in place. As described above, an alternative embodiment ofthe invention includes yokes 16 which are separate entities from thefixation members 14, and are polyaxially securable to the fixationmembers 14. If such separate polyaxially securable yokes 16 areincluded, tightening of the set screws 18 may also press the endcouplings 28 and end caps 120 against the heads 142 of the fixationmembers 14, thereby restricting further rotation of the polyaxiallysecurable yokes 16 with respect to the fixation members 14 to secure theentire assembly. Those of ordinary skill in the art would readilyrecognize this operation.

Referring to FIG. 9, two assembled stabilizers 12 are illustratedpositioned end-to end with two end caps 120 positioned at the outer endsof the stabilizers 12. Two stabilizers 12 may be interlocked with eachother end-to-end and implanted when it is desirable to stabilize therelative motion of three adjacent vertebrae. FIG. 10 depicts a similarassembly, with two stabilizers 12 being illustrated end-to-end, and oneend cap 120 being secured to each outer end coupling 28 in a similarfashion to that previously depicted in FIG. 7. On the inner ends of eachstabilizer 12, the teeth 112 of each end coupling 28 are aligned to fitinto the notches 114 of the facing end coupling 28. FIG. 11 depicts thetwo stabilizers 12 in an end-to-end fashion and partially interlockedtogether. The teeth 112 of each facing end coupling 28 are in thenotches 114 of the opposite end coupling 28, and the stabilizers 12 havebeen partially turned so that the teeth 112 are partially interlocked.In FIG. 12, the two stabilizers 12 are shown completely interlockedend-to-end. The end couplings 28 of the two stabilizers 12 are rotatedinto locking engagement with each other and an end cap 120 is lockedonto each unoccupied external end coupling 28. The entire dynamicstabilization assembly has four articulation components 24, 25, whichwill permit considerable differentiation in orientation between thethree fixation members 14 that would be used to attach the stabilizers12 to three adjacent vertebrae (not shown). In fact, in FIG. 13, twointerlocked stabilizers 12 are illustrated with the articulationcomponents 24, 25 in an articulated position so that the stabilizers 12no longer lie in a straight line, but instead the multi-level dynamicstabilization assembly approximates a curve. This enables the assemblyto conform to the desired lordotic curve of the lower spine or to otherspinal curvatures, such as those caused by or used to correct scoliosis.Additional levels can be added if desired.

Referring to FIG. 14, a stabilizer 12 is depicted secured end-to-end toa rigid connector 160 to provide dynamic stabilization across one level,and posterior immobilization and/or fusion across the adjacent level.The rigid connector 160 has a rod 162 and an end coupling 164. The endcoupling 164 is toothed and notched so that it may engage the endcoupling 28 on the stabilizer 12. This is not unlike the other couplingsdiscussed above. In addition, and like that discussed above, the rod 162may be secured in the yoke 16 of a fixation member 14 with a set screw18. Similarly, the interlocked end coupling 164/end coupling 28combination may be secured in the yoke 16 of an anchoring member 19 in amanner similar to the previously described securing of the end couplingsand end caps. Additional rigid connectors 160 or stabilizers 12 withassociated anchoring members 19 can be added if additional levels aredesired.

FIG. 15 depicts an exploded view of the system depicted in FIG. 14,having one stabilizer 12, an end cap 120, and one rigid connector 160.The end coupling 164 has teeth 166 protruding from one end, and notches167 between the teeth. When the rigid connector 160 is attached to thestabilizer 12, the teeth 166 of the end coupling 164 fit into thenotches 114 of the end coupling 28. Simultaneously, the teeth 112 of theend coupling 28 fit into the notches 167 of the end coupling 164. Thestabilizer 12 and the rigid connector 160 are rotated in oppositedirections so that the teeth 112, 166 interlock and the stabilizer 112and the rigid connector 160 are locked together. The end cap 120 isinterlocked onto the remaining open coupling 28 of the stabilizer 12 aspreviously described. FIG. 16 depicts one stabilizer 12 interlocked witha rigid connector 160 and an end cap 120, and in a position withcomponents 24, 25 being articulated to allow the assembly to approximatea curve.

Thus, like the above described systems, dynamic stabilization across onelevel and posterior immobilization and/or fusion across the adjacentlevel may be accomplished while simultaneously following the desiredcurvature of the spine. In some cases, it may be desirable to allowimmobilization and/or fusion across one level, and dynamic stabilizationacross the adjacent level on each end. In such a case, a rigid connector160 with an end coupling 164 at each end could be used, allowing astabilization module 12 to couple to each end of the rigid connector160.

Referring to FIG. 17, an alternative embodiment of a stabilizationsystem 168 is depicted. In this system, a stabilizer 170 is secured totwo anchoring members 19. As in the previous embodiment, the anchoringmembers 19 each preferably include two yokes 16 connected with twofixation members 14, and two set screws 18 are preferably used to holdthe stabilizer 170 in place.

As seen in FIG. 18, the stabilizer 170 has a spring casing 172 and twoarticulation components 174, 175. A two-piece end housing 178 alsopreferably extends from either articulation component 174, 175. As shownin FIG. 19, the spring casing 172 preferably houses a planar spring 180.The planar spring 180 has a first side 182 and a second side 183.Extending from the first side 182 is an arm 184 which narrows into aneck 186 and terminates in a semispherical surface 188. The springcasing 172 has an outer hollow member 190 and an inner hollow member192. The inner hollow member 192 is of a shallow dish shape, and has acircular plate 194 which forms the base of the hollow member, with athreaded outer rim 196 which encircles the outside of the plate 194. Aninner rim 198 encircles a round hole 200 in the center of the plate 194.

Similarly, the outer hollow member 190 is of a deep dish shape with aninterior cavity 202. It has a circular plate 204 which forms the base ofthe hollow member, and a support member 206 which forms the side wall ofthe hollow member. An inner surface 208 of the support member 206 isthreaded, but a neck 210 extends from the outside of the plate 204 andterminates in a semispherical surface 212. This latter element isdifferent from both inner hollow member 192 and that which is includedin the above described embodiments of the present invention.

When assembled, the planar spring 180 preferably fits into the cavity202 of the outer hollow member 190, with the second side 183 adjacent tothe plate 204 of the hollow member 190. The inner hollow member 192 fitsover the planar spring 180, so that the arm 184 and the semisphericalsurface 188 extend through the hole 200 in the inner hollow member 192.Thereafter, the threads on the outer rim 196 engage with the threads onthe inner surface 208 of the outer hollow member 190, joining the hollowmembers 190, 192 to form the casing 172. The spring 180 is thuslycaptured inside the casing 172, which prevents it from moving axially.When the arm 184 moves toward or away from the outer hollow member 190,the planar spring 180 extends out of its plane. When the arm 184 returnsto its original position, the planar spring 180 recoils back towards itsplane. During this extension and recoiling, the plate 194 of the innerhollow member 192 and the plate 204 of the outer hollow member 190 actas barriers to limit the movement of the planar spring 180. The arm 184is encircled by the inner rim 198, which acts as a bearing surface toprevent radial movement of the arm relative to the inferior hollowmember 192.

As seen in FIG. 20, a coupling in the form of a two-part end housing 178fits over each semispherical surface 188, 212. Each end housing 178 hasa first wall 220 and a second wall 222. The first wall 220 is shapedlike a segment of a cylindrical body that is split lengthwise, and hasan inner surface 224 and rounded outer surface 226. At each lengthwiseend of the first wall 220, a rounded first hollow 228 is indented intothe inner surface 224. Indented into the inner surface 224, between thehollows 228, are two receiving holes 230. The second wall 222 is alsoshaped like a segment of a cylindrical body and has an inner surface 234and an outer surface 236. Unlike the first wall 220, the outer surface236 is not rounded but is squared off so it is flat. The inner surface234 has a rounded second hollow 238 indented into each lengthwise end.Each pair of rounded hollows 228, 238 cooperates to define a socketsized to receive the corresponding ball 188 or 212. Two pin holes 240extend from the outer surface 236 through the wall 222 to the innersurface 234, such that two pins 242 can fit through the pin holes 240and into the receiving holes 230 in the first wall 220. The pins 242 andreceiving holes 230 releasably hold the walls 220, 222 together aroundthe semispherical surfaces 188, 212, and prevent shearing of the walls.In other embodiments of the invention, the pins 242 and receiving holes230 could be replaced by posts and brackets, or a snap mechanism orother mechanisms capable of releasably joining the walls 220, 222.

The assembled stabilizer 170 fits into the yokes 16 of two anchoringmembers 19, as is best shown in FIG. 17 (shown disassembled in FIG. 21).In the fully assembled state, the end housings 178 are preferablysituated perpendicular to the fixation members 14, so that the endhousings 178 fit between support walls 144 of anchoring member 19, andthe rounded outer surface 226 is cradled on a curved floor 142 betweenwalls 144. Two set screws 18 are thereafter engaged in the threads 150and tightened. The tightening of the set screws 18 creates pressure onthe end housings 178, holding the housings closed around thesemispherical surfaces 188, 212. As described in the previousembodiment, each anchoring member 19 may comprise a unitary piece whichincludes both the fixation member 14 and the yoke 16, or the fixationmember 14 and the yoke 16 may be separate pieces. In such an embodimentwhere the fixation member 14 and yokes 16 are separate pieces,tightening of the set screws 18 may also press the end housings 178against the heads 142 of the fixation members 14, thereby restrictingfurther rotation of the yokes 16 with respect to the fixation members 14to secure the entire assembly.

Like the above embodiment, two stabilizers 170 can be secured end-to-endin accordance with this latter embodiment. When two stabilizers 170 areto be used together, the stabilizers are partially assembled as shown inFIG. 19 and described previously. The semispherical surface 212 or 188from one stabilizer 170 is preferably placed in the empty hollow 228 ofthe first wall 220 of the second stabilizer 170 before the second wall222 is joined to the first wall 220. When the second wall 222 is joinedto the first wall 220, the semispherical surfaces 212, 188 are capturedin the socket sections 228, 238 and the modules are joined. A stabilizer170 can also be employed in combination with a rigid connector toprovide dynamic stabilization across one level and posterior fusionacross the adjacent level. Additional levels may be added as desired.Multiple stabilization/fusion levels can include two or more sequentialrigid connectors, or rigid connectors sequentially interspersed withstabilizers.

Referring to FIG. 22, a portion of an “overhung” dynamic stabilizationsystem is shown. This system can be used when an offset between adjacentfixation members is desired and/or when a short pedicle-to-pedicledisplacement must be accommodated. In this embodiment, a stabilizer 250includes a housing 252, an articulation component 254 and an arm 256which extends from the joint. A tunnel 258 provides an opening forplacement of the stabilizer 250 over an anchoring member (best shown inFIG. 26), and two set screws 259 are used to press a flexible stop 260against the anchoring member, securing the stabilizer 250 in place.

FIG. 23 depicts an exploded view of the stabilizer 250 in more detail.As shown in that figure, the housing 252 has a chamber 262 which holdsthe articulation component 254. A threaded cap 264 is screwed into thehousing 252 closing off one end of the chamber 262. A planar spring 266with a threaded inner ring 268 is positioned within the cap 264.Releasably screwed to the inner ring 268 is a socket 270 with a threadedend stud 272. A cup 274 terminates the socket 270 at the end oppositethe threaded end stud 272. A semispherical surface 276 is connected tothe arm 256, and the semispherical surface 276 rotatably rests in thecup 274. A tubular sleeve 278 surrounds the socket 270, semisphericalsurface 276 and arm 256. The sleeve 278 has a central bore 280 throughwhich the arm 256 protrudes. The sleeve 278 also has two grooves 282which run lengthwise down opposite outer sides of the sleeve. When thesleeve 278, along with the enclosed socket 270, semispherical surface276 and arm 256 are in the chamber 262, the sleeve is held in place bytwo pins 284. The pins 284 are inserted through two pin holes 286 whichperforate the outer wall of the housing 252. The inserted pins 284 fitinto the grooves 282, and prevent the sleeve 278 and its enclosedcontents from moving axially.

An unassembled stabilization system 248 is shown in FIG. 24. The system248 includes the overhung stabilizer 250, an anchoring member 19, ananchoring member 288, an articulation component 24, an end coupling 28and an end cap 120. As described in previous embodiments, the anchoringmember 19 has a fixation member 14, a yoke 16 and a set screw 18. Theanchoring member 288 comprises a fixation member 14 and an extensionpost 290. Once again, the fixation members 14 may comprise pediclescrews, screws fixed to other parts of the vertebrae, pins, clips,clamps, adhesive members, or any other device capable of anchoring thestabilizer to the vertebrae. Additionally, each yoke 16 may be unitarilyformed with a fixation member 14 as illustrated herein, or each yoke 16may be a separate entity and be polyaxially securable to a fixationmember 14. The articulation component 24 has a tubular joining arm 292extending from an end coupling 28. The joining arm 292 is shaped to fitover the end of the arm 256 which protrudes from the articulationcomponent 254.

FIG. 25 illustrates the stabilization system 248 in a partiallyassembled state. The stabilizer 250 is joined to the articulationcomponent 24 and end coupling 28, with the joining arm 292 fitting overthe end of the arm 256 which protrudes from the articulation component254 through the use of a press fit or other attachment mechanism. Theend cap 120 fits on the opposite end of the end coupling 28, in themanner previously described. The fully assembled stabilization system248 is shown in FIG. 26. In this assembly, the end coupling 28 and endcap 120 fit in the yoke 16 of the anchoring member 19, and are held inplace by tightening the set screw 18, in the same manner set forthpreviously. The assembled stabilizer 250 is placed over the anchoringmember 288, with the extension post 290 on the anchoring member 288extending posteriorly through the tunnel 258. The set screws 259 areengaged in the outer wall of the housing 252 adjacent to the extensionpost 290. When the set screws 259 are tightened, they push against theflexible stop 260, which in turn pushes against the post 290, holdingthe stabilizer 250 in place on the extension post 290. Finally, thejoining arm 292 connects the articulation component 24 to thearticulation component 254, thus pivotably connecting the stabilizer250, secured to the anchoring member 288, to the anchoring member 19.

When the system 248 is fully assembled and anchored to two adjacentvertebrae, motion between the two vertebrae can cause the planar spring266 to flex out of its plane. Referring back to FIG. 23, when the twoadjacent vertebrae move closer together and the distance between themshortens, the planar spring 266 returns to its plane. When the twoadjacent vertebrae move apart and the distance between them lengthens,the planar spring 266 flexes in the opposite direction along the spiralpath, toward the sleeve 278. As the planar spring 266 flexes, the sleeve278 which holds the articulation component 254 slides along the chamber262. The grooves 282 allow the sleeve 278 to slide back and forth pastthe pins 284, but the pins 284 restrict axial movement of the sleeve 278and serve as stops to prevent the sleeve 278 from moving completely outof the chamber 262.

Referring to FIG. 27, a multi-level dynamic stabilization system isshown which includes a stabilizer 12 as per FIGS. 1-8, and an overhungstabilizer 250 as per FIGS. 22-26. The stabilizer 12 is mounted on twoanchoring members 19 and connected via the joining arm 292 to theoverhung stabilizer 250 which is mounted an anchoring member 288. Theresulting dynamic stabilization system provides stabilization across twoadjacent vertebral levels. The overhung stabilizer 250 allows one of thelevels to have a relatively short pedicle-to-pedicle displacement. FIG.28 illustrates the stabilizers 12, 250, two anchoring members 19 and oneanchoring member 288 in an exploded view. Each anchoring members 19includes a fixation member 14, a yoke 16 and a set screw 18, as setforth previously. The anchoring member 288 includes a fixation member 14with an extension post 290, as set forth previously.

Referring to FIG. 29, the stabilizers 12, 250 and the anchoring members19, 288 are shown in a further exploded view. The stabilizer 12 has twoend couplings 28, one end coupling 28 connecting with one end cap 120thereby forming a coupling mountable in a yoke 16. The second endcoupling 28 of the stabilizer 12 preferably couples with the endcoupling 28 that connects to the joining arm 292, forming a couplingmountable in another yoke 16. The joining arm 292 fits over the arm 256of the stabilizer 250, thus connecting the stabilizer 250 to thestabilizer 12. The stabilizer 250 is mountable on the anchoring member288, in the manner set forth previously. When assembled, this two levelsystem has two articulation components 24, one articulation component25, and one articulation component 254, providing pivotability betweenthe stabilized vertebrae. Additionally, an overhung stabilizer 250, astabilizer 12, and/or a stabilizer 170 such as that depicted in FIGS.17-21 can be implanted in combination with a rigid connector 160 such asthat depicted in FIGS. 14-16.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

The invention claimed is:
 1. A stabilization system for controllingrelative motion between a first vertebra and a second vertebra, thestabilization system comprising: a first stabilizer including: a firstcoupling adapted to be attached to a first anchoring member; a secondcoupling adapted to be attached to a second anchoring member; and aresilient member configured to be coupled to the first and secondcouplings to transmit resilient force between the first and secondcouplings, the resilient member including a planar spring, wherein atleast a portion of the planar spring is predisposed to resist flexionwhen being moved out-of-plane in response to relative motion between thevertebrae and wherein at least the first coupling is attached to acenter portion of the planar spring, the first coupling being spacedfrom a peripheral portion of the spring.
 2. The stabilization system ofclaim 1, wherein the first stabilizer further includes a casingincluding a hollow first member and a hollow second member, wherein theresilient member is positioned within a cavity defined by engagement ofthe first and second hollow members.
 3. The stabilization system ofclaim 2, wherein the resilient member is positioned inside the casingsuch that the casing limits relative motion of the vertebrae by limitingdeflection of the planar spring.
 4. The stabilization system of claim 1,further comprising the first anchoring member and the second anchoringmember.
 5. The stabilization system of claim 4, wherein each of thefirst and second anchoring members includes a yoke polyaxially coupledto a fixation member implantable in a portion of either the first orsecond vertebra.
 6. The stabilization system of claim 1, furthercomprising a first rigid connector including first and second couplingsadapted to be attached to one of the first and second anchoring members,wherein the couplings are substantially rigidly connected together. 7.The stabilization system of claim 1, wherein the path followed by theplanar spring is generally spiral-shaped, and wherein the planar springincludes the peripheral portion attached to the second coupling.
 8. Thestabilization system of claim 1, wherein the first stabilizer furtherincludes a first articulation component configured to articulate topermit polyaxial relative rotation between one of the first or secondcouplings.
 9. The stabilization system of claim 8, wherein the firstarticulation component includes a semispherical surface and a socketwithin which the semispherical surface is rotatable to permit polyaxialmotion between the resilient member and the first anchoring member. 10.The stabilization system of claim 1, wherein the resilient member iscoupled to the first and second couplings such that the resilient memberis able to urge the first and second couplings to move closer togetherand is also able to urge the couplings to move further apart.
 11. Thestabilization system of claim 1, further comprising a second componentcomprising a third coupling and a fourth coupling, wherein the thirdcoupling is adapted to be attached to the first anchoring member suchthat the first anchoring member is capable of simultaneously retainingthe first and third couplings.
 12. The stabilization system of claim 11,wherein the second component includes a rigid connector, wherein thethird and fourth couplings are substantially rigidly connected together.13. The stabilization system of claim 11, wherein the second componentincludes a second stabilizer comprising a second resilient memberconfigured to exert resilient force between the third and fourthcouplings.
 14. A stabilization system for controlling relative motionbetween a first vertebra and a second vertebra, the stabilization systemcomprising: a first stabilizer including: a first coupling adapted torest within a yoke of a first anchoring member; a second couplingadapted to rest within a yoke of a second anchoring member; a resilientmember coupled to the first and second couplings to transmit resilientforce between the first and second couplings, the resilient memberincluding a planar spring, wherein at least a portion of the planarspring is predisposed to resist flexion when being moved out-of-plane inresponse to relative motion between the vertebrae; and a firstarticulation component configured to articulate to permit relativerotation between the first stabilizer and one of the first or secondcouplings.
 15. The stabilization system of claim 14, further comprisinga second component including a third coupling and a fourth coupling,wherein the third coupling is adapted to be attached to the firstanchoring member such that the first anchoring member is capable ofsimultaneously retaining the first and third couplings.
 16. Thestabilization system of claim 15, wherein the second component includesa rigid connector, wherein the third and fourth couplings aresubstantially rigidly connected together.
 17. The stabilization systemof claim 15, wherein the second component includes a second stabilizerhaving a second resilient member configured to exert resilient forcebetween the third and fourth couplings wherein the first stabilizerfurther includes a casing comprising a hollow first member and a hollowsecond member, the resilient member being positioned within a cavitydefined by engagement of the first and second hollow members.
 18. Thestabilization system of claim 14, wherein the yoke of each of the firstand second anchoring members is polyaxially coupled to a fixation memberimplantable in a corresponding vertebra.
 19. The stabilization system ofclaim 14, wherein the first articulation component includes asemispherical surface and a socket within which the semisphericalsurface is rotatable to permit polyaxial motion between the resilientmember and the first anchoring member.
 20. The stabilization system ofclaim 14, wherein the resilient member is coupled to the first andsecond couplings such that the resilient member is able to urge thefirst and second couplings to move closer together and is also able tourge the couplings to move further apart.
 21. A stabilization system forcontrolling relative motion between a first vertebra and a secondvertebra, the stabilization system comprising: a first stabilizerincluding: a first coupling adapted to be attached to a first anchoringmember; a second coupling adapted to be attached to a second anchoringmember; a resilient member configured to be coupled to the first andsecond couplings to transmit resilient force between the first andsecond couplings, the resilient member including a planar spring,wherein at least a portion of the planar spring having a generallyspiral-shaped path is predisposed to resist flexion when being movedout-of-plane in response to relative motion between the vertebrae; afirst articulation component configured to articulate to permit relativerotation between the first and second couplings; and a first rigidconnector including third and fourth couplings adapted to be attached tothe first and second anchoring members, wherein the third and fourthcouplings are substantially rigidly connected together.
 22. Thestabilization system of claim 21, wherein each of the first and secondanchoring members includes a yoke polyaxially coupled to a fixationmember implantable in a corresponding vertebra, wherein the firstcoupling is adapted to rest within the yoke of the first anchoringmember, and the second coupling is adapted to rest within the yoke ofthe second anchoring member.
 23. The stabilization system of claim 21,wherein the first stabilizer further includes a casing comprising ahollow first member and a hollow second member, wherein the resilientmember is positioned within a cavity defined by engagement of the firstand second hollow members.
 24. The stabilization system of claim 21,wherein the first articulation component includes a semisphericalsurface and a socket within which the semispherical surface is rotatableto permit polyaxial motion between the resilient member and the firstanchoring member.
 25. The stabilization system of claim 21, wherein theresilient member is coupled to the first and second couplings such thatthe resilient member is able to urge the first and second couplings tomove closer together and is also able to urge the couplings to movefurther apart.
 26. The stabilization system of claim 21, furthercomprising a second component comprising a fifth coupling and a sixthcoupling, wherein the fifth coupling is adapted to be attached to thefirst anchoring member such that the first anchoring member is capableof simultaneously retaining the first and fifth couplings.